Modern electrochromic devices generally comprise a number of layers such as is shown in FIG. 1 of U.S. Pat. No. 4,193,670. One example of such a device is: a backing of a pane of glass first coated with an electronic conductor such as a thin transparent layer of indium/tin oxide to form what some call a front electrode or a working electrode; then the working electrode is coated with a thin transparent layer of tungsten oxide to form an electrochromic layer; then the electrochromic layer is coated with a thin transparent layer of an ion conducting polymer (see U.S. Pat. No. 4,231,641) such as NAFION perfluorosulfonate polymer (from E.I. Du Pont de Nemours and Company, Wilmington Del.) to form an ion conducting layer; and finally the ion conducting layer is coated with a thin transparent coating of gold to form a counter electrode. The completed device usually has the appearance of lightly tinted transparent glass. The device can be made to transmit substantially less light by applying an electrical potential between the working electrode and the counter electrode. This effect can be reversed by reversing the electrical potential. The theory of operation of such a device is: (1) that hydrogen ions and electrons are forced from the ion conducting layer into the electrochromic layer by the electrical potential and form a highly colored hydrogen/tungsten oxide bronze in the electrochromic layer; and (2) when the electrical potential is reversed, the hydrogen ions of the hydrogen/tungsten oxide bronze in the electrochromic layer and electrons are forced out of the electrochromic layer into the ion conducting layer converting the highly colored hydrogen/tungsten oxide bronze back into the essentially colorless tungsten oxide.
A problem with such devices is that when they are operated at high temperature, then the device does not darken sufficiently, if at all, to be useful when the electrical potential is applied between the working electrode and the counter electrode.